For anyone unfamiliar with Humble Book Bundle, it is pretty simple. They run a special for two weeks and you pay whatever you want for the basic books available (minimum might be $1 not free, but I'm not sure) and you can pick how the money you pay is divided between the content creators, selected charities, and Humble Bundle itself. Then there are additional books available if you pay over the average (typically increasing over time) or over a set minimum. After one week, additional books are always added to the bundle, but if you buy in the first week you automatically get the new stuff. The files are always completely DRM free and you get them in multiple formats (epub, mobi, pdf and HD pdf for comics).

The comics (and a bonus game) available this time are:

For Any Price- Series 1 Vol. 1-3 (17 single issues for three complete David Tennant adventures)- Series 2 Vol. 1-4 (17 single issues for four complete Matt Smith adventures)- A Doctor Who game for Android devices only

For over the average (Currently c. $8)- Series 3 Vol. 1-4 (17 single issues for four more complete Matt Smith adventures)

For over $15- Prisoners of Time Vol. 1-3 (12 Issues - I've read this one and it is fun for Classic and Nu Who fans. It was released for the 50th anniversary and each issue is a different doctor, 1-11, on a silly adventure that ends with companions being kidnapped as a big villain is messing with the Doctor in multiple timelines Issue 12 is the big multi-Doctor rescue, wrap up, etc.).- The 2013 Doctor Who Special Issue, The Girl Who Loved Doctor Who which is meta with the real Doctor meeting an actor named Matt Smith who plays him in a TV show.

This is a really good deal, so if you have any interest in Doctor Who comics at all, you should head over there now.